Nearly all motor vehicles today are provided with inflatable restraint systems to protect both the driver and passengers in the event of a collision. The air bag system for the passenger side of the vehicle generally includes an inflator and reaction canister located behind the instrument panel and the air bag inflates through an opening in the panel through which the air bag deploys. That opening may be covered by a generally rectangular shaped door that is flush-mounted in the opening and is moved out of the way on a hinge or tethers by the deploying air bag. In newer applications, the door that covers the opening may be “invisible” to the occupants of the vehicle, that is, hidden behind a surface covering of skin and foam which is pre-weakened by a groove formed on the backside of the skin layer to allow a predictable tearing of the skin. A separate door substrate may be located beneath the skin and foam layers and is hinged or tethered to the instrument panel or canister to control door opening.
Vehicles such as small trucks, SUV's and small to medium sized cars often will use a hard panel construction, i.e., without a separate soft skin and padded foam layer, to reduce cost. In these cases, a separate air bag door, instrument panel and door chute may be assembled over the canister. To control the path of the air bag as it expands, a deployment chute transitions the space between the canister where the bag is stored and the back of the air bag door to assure that the bag does not expand in an undesirable direction. Use of a hard door separate from the remainder of the instrument panel may allow replacement of only the door portion after a low speed deployment, as the remainder of the instrument panel may not be damaged. In still other applications, the hard instrument panel and door may be formed of unitary construction with a pre-weakened seam of reduced cross-section formed on the underside of the panel, outlining at least a portion of the periphery of the air bag door. Hinges, tethers, reinforcements and chutes may then be post-attached to the molded hard panel. This unitary construction is preferred as aesthetics are enhanced (no visible seam) and cost is reduced (a single molding rather than multiple components assembled together). Optionally, a substrate and air bag door portion molded of unitary construction may be covered with a skin layer or skin and foam layer to provide a soft trim panel with hidden air bar door.
Additionally, it is known in the art to use both hinges and tethers to control the opening and travel of the door or door substrate. In U.S. Pat. Nos. 5,685,930; 5,564,731; 5,804,121; 5,902,428 and 5,975,563 to Gallagher, et al. and commonly assigned to the assignee of the present invention and included herein by reference, a molded motor vehicle instrument panel made of thermoplastic material having an integral air bag deployment door for a passenger side air bag that is defined by a tear seam and normally retained by a hinge flange is disclosed.
In U.S. Pat. Nos. 5,685,930 and 5,902,428, upon deployment the door is retained by a supplemental flexible tethering hinge which is formed separately from the panel and attached by welding or an adhesive. The supplemental tethering hinge contains a loop or fold 63 as slack to let the door separate and move controllably away from the instrument panel to allow the bag to expand through the opening.
In U.S. Pat. Nos. 5,564,731 and 5,975,563 the flexible tethering hinge is described as being of sheet material, thermosetting, thermoplastic, metal mesh or woven fabric of plastic or natural fibers and attached by mechanical fasteners or hot staked bosses on the inner side of the door portion.
U.S. Pat. Nos. 5,975,563 and 5,804,121 are directed at an integral mounting hinge/flange on which is formed a bonded layer of a second plastic material on one side of the flange as well as and on the inner side of a potentially frangible portion of the door. The second plastic material has the physical characteristic of remaining ductile at low temperature at which the instrument panel plastic material becomes brittle, and as a result, the bonded layer forms a tether to retain the door in a controlled manner as it separates from the instrument panel when the air bag is deployed.
In U.S. Pat. No. 5,765,862 to Autoliv ASP, Inc., an inflatable air bag assembly mounted in a rectangular opening in the vehicle instrument panel is disclosed having bracket means, a plurality of thermoplastic resin fasteners and an integrally formed tether support bar 18 for a tether 20 that is connected between the door 14 and a bracket 22, on the air bag module 16.
U.S. Pat. No. 5,533,746 to Morton International recites a cover for covering an opening in a panel adjacent to an air bag inflation system comprising a tether attachment element having a first portion sandwiched between said inner (metal) and outer substrates and a second portion exposed for attachment to a tether, and at least one tether having a loop at an outer end portion of said tether attachment element and having an inner end portion adapted for fixed attachment to limit the amount of movement of said cover away from the opening deployment of the air bag inflation system. The tether may comprise a loop and the attachment element may be an elongated metal rod. The attachment element (rod) has a series of “U-shapes” that extend between the door inner and outer back to a flexible tether that is looped in its undeployed condition.
U.S. Pat. No. 5,332,257, also to Morton International, discloses a tether having first and second ends, the first end being secured to said module cover (on the B-side), and the second end forming a loop. A retainer rod extends through said loop and a channel encloses said retainer rod and loop in a fixed position to anchor said tether.
U.S. Pat. No. 5,211,421 to G.M., discloses a tether that is on the A-side of an air bag door, between substrate and foam layer which is fastened to a bracket on the canister.
All of these references use numerous components, particularly separate tethers, in an attempt to accomplish their objectives resulting in added material and manufacturing costs. Separate door, chute, tether, fasteners and reinforcement materials are combined with a myriad of attachment processes to form an assembly that may be installed in the instrument panel.
It is therefore an object of this invention to provide a tether for an air bag door that is integrally formed within the unitary molding of the door and adjoining panel to retain the air bag door upon air bag deployment, wherein an improved construction for the functioning of the tether comprises a stiffening frame and/or deployment chute attached to the backside of the trim panel just outboard of the air bag door tear seam (or area of reduced cross-section).
It is a further object of the present invention to provide a tear seam of reduced cross-section which defines at least a portion of the air bag door as well as the integrally formed tether(s), which interacts with the attached stiffening frame.
It is a still further object of this invention to provide a tether that includes a tear stop which prevents the air bag door from completely separating from the adjacent panel upon air bag deployment, which interacts with the attached stiffening frame.
It is a still further object of the present invention to outline the aforementioned tether and tear stops generally in the shape of a “U”, preferably as a dovetail in which the base of the “U” is wider than the open end of the “U”, so that that the propagation of tearing along the area of reduced cross-section do not converge into the area forming the tether.
It is a still further object of the present invention to provide a stiffening frame that may be mounted on the top side of the trim panel and attached through the panel to the underlying deployment chute.
It is therefore an object of the present invention to provide an improved construction for the functioning of the tether of the present invention which comprises a stiffening frame and/or deployment chute attached to the backside and/or frontside of the trim panel just outboard of the air bag door tear seam (or area of reduced cross-section). The means of attachment of the stiffening frame is constructed so as not to engage with the tether to allow for additional displacement of the door from the panel. These and other objects, advantages and features of the present invention will become more apparent form the following description and accompanying drawings.